physics 121: electricity & magnetism – lecture 10 carsten denker njit physics department...
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Physics 121: Electricity & Magnetism – Lecture 10
Carsten Denker
NJIT Physics DepartmentCenter for Solar–Terrestrial
Research
March 28, 2007 Center for Solar-Terrestrial Research
Magnetic Field Due to a Current
Long straight wireSemi–infinite straight wire
Circular arc
Biot–Savart’s law
Permeability constant
034
ids rdB
r
70 4 10 Tm/A
0
4
iB
R
0
2
iB
R
0
4
iB
R
March 28, 2007 Center for Solar-Terrestrial Research
Force Between two Parallel Currents
To find the force on a current–carrying wire due to a second current–carrying wire, first find the field due to the second wire at the site of the first wire. Then find the force on the first wire due to that field.
Parallel currents attract, and anti– parallel currents repel.
March 28, 2007 Center for Solar-Terrestrial Research
Ampere’s Law
Ampere’s law
Curl your right hand around the Amperian loop, with the finger pointing in the direction of integration. A current through the loop in the general direction of your outstretched thumb is assigned a plus sign, and a current generally in the opposite direction is assigned a minus sign.
0 encB ds i
March 28, 2007 Center for Solar-Terrestrial Research
Solenoids and Toroids
Ideal solenoid
Toroid
0B in
0 1
2
iNB
r
March 28, 2007 Center for Solar-Terrestrial Research
Current–Carrying Coil as a Magnetic Dipole
Current–carrying coil
032
B zz